Female blue tits who play the field to avoid the chances of inbreeding produce sexier sons and more fertile daughters, says new German research.

Researchers at the Max Planck Research Centre for Ornithology in Starnberg, Germany report in Nature that female blue tits prefer more than one mate to improve their chances of producing fitter young, a finding that could have implications for better understanding human sexual behaviour.

"I believe there is no reason that the theory we have for birds couldn't apply to humans. It applies to other mammals," says Dr Bart Kempenaers, a behavioural ecologist at the centre.

"We know that this social monogamy does not actually reflect the mating that is going on," he told Reuters in an interview.

Kempenaers and his team uncovered the randy behaviour while studying blue tits that were breeding in boxes in the Viennese Forest in Austria.

They noticed that when female birds were paired with young males they were more likely to be unfaithful with older or bigger males and that the young they produced were more likely to survive to the next breeding season.

When the offspring matured if they were females they produced more eggs than the other birds and if they were males they had a more attractive feather crown, a big draw with the ladies.

"Our research suggests that females are promiscuous, or unfaithful to their partners, to avoid negative effects of in-breeding," Kempenaers says.

He believes the female birds have a way of assessing the quality of their partner and if they are not happy, they look elsewhere for potential mates. "We have good observations to show it is really the females that are playing the active role."

It's not exactly a night out on the town, but the researchers spotted female birds going out early in the morning when it was still dark and when all the males were singing in the dawn chorus.

"It is during these early morning hours when they are fertile they go out and seem to look for particular males to copulate with," he adds.

The next big question the researchers hope to answer is whether promiscuity in females has some sort of genetic basis or whether it is related to personality.

Kempenaers says fidelity still exists in some species, notably swans and sea birds such as the albatross that mate for life and are never unfaithful to their partners.